This invention relates in general to a method of making a fancy orange single crystal diamond material by post-growth treatment of a diamond material that has been grown by a CVD (chemical vapor deposition) process, and to CVD single crystal diamond material which is fancy orange in color.
The term “fancy-colored diamond” is a well-established gem trade classification and is used to refer to unusual colored diamonds. A useful history and background to the grading of fancy colored diamond gemstones, including the use of Munsell color charts is given by King et al, in Gems & Gemology, Vol. 30, No. 4, 1994 (pp. 220-242).
Examples of fancy colored synthetic and natural diamonds made by introducing color centers into the diamond are known in the prior art. For example, EP0615954A and EP0316856A describe irradiation of synthetic diamond material with an electron beam or a neutron beam to form lattice defects (interstitials and isolated vacancies) in the crystal. Thereafter the diamond crystal is annealed in a prescribed temperature range to form color centers. Neither of these publications discloses orange diamond material.
Another publication describing the formation of fancy colored diamond material is “Optical Absorption and Luminescence” by John Walker in “Reports on Progress in Physics”, Volume 42, 1979. That publication similarly describes the steps of forming lattice defects in crystals by electron beam irradiation, and if necessary annealing to cause the lattice defects to combine with nitrogen atoms contained in the crystals. There is no disclosure of orange diamond material in this publication.
US 2004/0175499 (Twitchen et al) describes a method starting with a colored CVD diamond, usually brown or near-brown, and applying a prescribed heat treatment to produce another and desirable color in the diamond. The prior art reference notes that the relative strengths of the absorption bands in the visible region of the spectrum of brown single crystal CVD diamond can be altered by annealing, with concurrent changes in the Raman spectrum, and that changes in the absorption spectrum are observed at much lower temperatures than are required to alter the color of brown natural diamond. Significant color changes are said to be achieved by annealing at atmospheric pressure in an inert atmosphere at temperatures of 1600° C. or less. One example describes a grown CVD diamond polished into a round brilliant of 0.51 carat that was graded as light brown. After annealing at 1700° C. for 24 hours it was graded as light orangish pink. Another example describes a grown CVD diamond slice which had an orange brown color, and after annealing this color becomes colorless. A further example describes a grown CVD diamond layer polished into a rectangular cut gemstone of 1.04 carats which is graded fancy dark orangey brown color. After annealing at 1600° C. for four hours this becomes a fancy intense brownish pink color.